China's first Mars exploration trip officially opened
Mars, here we are!
Mars, the red planet that has fascinated countless people, is about to welcome China's space messenger-Tianwen No.1.
On July 23, my country's first Mars probe Tianwen-1 was successfully launched by the Long March 5 carrier rocket. This marked the official start of China's first Mars exploration trip.
The successful launch is only the "first step in the Long March" of Tianwen's journey. Next, Tianwen-1 will have to fly about 7 months before reaching Mars.
Mars, here we are!
From "Three Rings" to "Four Rings"
In the solar system, the eight planets revolve around the sun, forming 8 circular orbits, of which the earth is located in the "third ring" and Mars is orbiting in the "four ring". In order for the Tianwen-1 probe to rush out of the earth to reach Mars, it is by no means a simple leap from the "third ring" to the "fourth ring", but a long journey for several months and a straight-line distance exceeding 400 million kilometers.
Cui Xiaofeng, the chief model officer of the Beijing Space Flight Control Center's first Mars exploration mission, told reporters that Tianwen-1 will go through the launching-in orbit section, the ground fire transfer section, the Mars capture section, the Mars mooring section, and the off-orbit landing section.
Among them, the fire transfer section refers to the flight phase from the separation of the probe and the rocket to the gravitational influence of Mars. This stage is the longest time-consuming part of the Tianwen-1 mission, which takes nearly 7 months.
In other words, starting from the successful launch on July 23, 2020, the time for Tianwen-1 to reach the orbit of Mars will be around February 2021.
Cui Xiaofeng said that after hundreds of millions of miles of raids, Tianwen-1 entered the Martian gravitational influence ball and was gradually captured by Mars. The probe's engine ignites and performs near-fire braking, lowers the probe's flight speed, leaned down, and successfully let Mars "catch" itself.
"Once it is successfully captured by Mars, the probe will orbit Mars and become a'fire orbiting satellite', and then enter the Mars mooring section." Cui Xiaofeng said.
According to him, the Mars mooring section is not anchored in the orbit of Mars, but flying around the fire in a polar orbit. This phase will last for several months, until the probe turns into the separation phase after the probe descends orbit.
Now that you have reached the orbit of Mars, why do you need to orbit for more than two months instead of directly falling into the "fire"?
"In a space mission, no gram of fuel is wasted for nothing, and no decision is meaningless." Cui Xiaofeng said that the flight around the fire at this stage is to help the ground control the high-resolution camera on the orbiter. The preferred landing area is to conduct detailed surveys and take photos for imaging.
After many rounds of accurate imaging, the flight controllers on the earth can see the "footprint" clearly, and then they can better control the Tianwen-1 to accurately land in the ideal area.
After seeing the target clearly, Tianwen-1 will start off-orbit landing. This stage is the key to the success or failure of Mars exploration missions, especially from entering the Martian atmosphere to landing, there is a world-famous "7 minutes of terror", not to mention the short time, but in the current more than 40 Mars exploration missions in the world Only 9 times have been able to spend these 7 minutes safely.
Cui Xiaofeng said that my country has to overcome this difficult process during its first Mars exploration mission and allow the rover to continue working on the fire surface for three months. The challenge is unprecedented.
Why go to mars
With such a big challenge and so difficult, why go to Mars? The world is so big, why choose it?
This is not a whim of two or three countries in the summer of 2020, but a common choice since human exploration of the planets in the 1960s: in the past few decades, humans have launched more than 40 probes to Mars, second only to the number Earth, and therefore, Mars has become the most popular "planetary travel destination" in the entire solar system. What is the point of marching on Mars? What value and meaning will exploring Mars bring?
All this starts with "who" Mars is.
In the solar system, Mars is the closest planet to the earth in its natural environment. Both were formed about 4.5 billion years ago and have the same composition, with a core, a mantle, and a crust. Mars and the Earth have a similar rotation cycle. A Martian day is about 24 hours and 39 minutes. Not only that, it also has four seasons like the Earth.
"Mars is the most similar to the Earth. Detecting and studying Mars plays an irreplaceable role in understanding our homeland of humanity-the Earth." said Liu Jizhong, deputy commander of China's first Mars exploration mission and director of the National Space Administration's Lunar Exploration and Space Engineering Center .
Of course, the difference between the two is obvious from the limited situation that mankind currently has. Liu Qian, an associate researcher at the Beijing Planetarium, said that Mars is smaller in appearance. Its radius is about half of the Earth, its volume is one-seventh of the Earth, and the atmospheric density is 1% of the Earth.
Unlike our blue planet, which has 71% ocean coverage, the surface of Mars appears red. At its brightest, it is like a fireball.
According to astronomers, this red is actually not a real flame, but the temperature on Mars is extremely low, close to the South Pole of the Earth. The reason for the red color is that the soil on Mars is rich in iron oxide, which is like rust on the ground. The formation of this kind of soil is caused by the double erosion of wind and water. This shows that there was a lot of water and atmosphere on Mars.
This means that life may have appeared on Mars. So, is Mars the past of the earth, or our future destination? This question aroused strong curiosity of scientists.
In an interview with reporters, Geng Yan, director of the General Department of Deep Space Exploration of the National Space Administration's Lunar Exploration and Space Engineering Center, said that previous explorations have found evidence of the existence of water, whether there are conditions for life on Mars, and whether Mars is the past of the earth or The future of the earth has become a major scientific issue for Mars research. The study of Mars has very important comparative significance for understanding the evolution of the earth.
And these questions can only be answered step by step if humans or human detectors are "immersive". Because of this, almost all human missions to Mars have received widespread attention.
Now this time, it is Tianwen No.1 from China.
Less than 50% success rate
Before the last moment of the "fire", the nervousness of the Chinese astronauts affected by the Tianwen-1 is difficult to completely relax.
Geng Yan said that for decades, the success rate of human Mars exploration has been less than 50%. The Soviet Union conducted nearly 20 detection missions between 1960 and 1988, but none of them were completely successful. After the 1990s, the success rate reached about two-thirds.
The Tianwen-1 probe developed by China Aerospace Science and Technology Corporation includes three parts: orbiter, lander, and patrol. The goal is to achieve three detection missions of "circumnavigation" in a single launch, which is the first in the world.
"Tianwen-1 did not follow the'old path' of the United States and Russia in Mars exploration. Therefore, this challenge has increased the difficulty of the mission." said the Tianwen-1 probe development expert of the China Aerospace Science and Technology Group Fifth Academy.
According to experts from the Fifth Academy, the atmospheric density of Mars is only about 1% of that of the Earth, and it can be used to slow down the probe, but the process will generate heat as high as 2000 degrees Celsius. The Mars lander not only needs a heat shield to insulate heat, but also needs to be equipped with deceleration and parachutes to further decelerate.
However, these are not enough to decelerate the detector to a level that can achieve a soft landing. In addition, a reverse thrust engine is required to decelerate to achieve hovering, obstacle avoidance, and landing. To put it simply, "landing is extremely difficult."
In addition, the choice of landing area and timing is also a major challenge. Experts from the Fifth Academy told reporters that the surface of Mars is full of ravines and gravel, which puts forward higher requirements for the choice of landing sites and the path planning of the rover. Due to the long-term weathering and lack of the greenhouse effect, the pressure difference between different areas of Mars is very large, which further leads to strong winds on the surface of Mars and frequent dust storms.
The issue of time delay has also attracted much attention. Cui Xiaofeng said that the Mars rover can be up to 400 million kilometers away from the earth, and a signal can travel between the earth and the spacecraft for up to 44 minutes. The extremely large time delay prevents the ground from using the real-time comparison and judgment closed-loop control mode in previous missions. After determining the execution of the instruction, follow-up actions are implemented according to the effect of the instruction execution.
According to him, in order to overcome this obstacle, the Beijing Flight Control Center adopted the ultra-large variable delay open-loop control technology and designed a new ultra-long-distance station acquisition mode. For example, when the flight controller issues an order, it is not aimed at the current position of the spacecraft, but at the position it reached when receiving the order 20 minutes later, so that it can be received when it is in place.
Although the Mars rover has a certain degree of autonomy, the destination, the path it chooses, and the various actions on the way need to be told in advance by the staff on the earth.
In this regard, the flight control team of our country must play the role of a "prophet", and predict the safety of the path through the mastery, analysis and planning of the current environment of the rover, otherwise the rocks and sand dunes may cause fatal injuries to it. .
Cui Xiaofeng said that now, as Tianwen-1 enters the ground fire transfer orbit, the flight control team has also completed the fire surface teleoperation condition evaluation and state prediction technology, deep space exploration interferometry technology and other difficult problems. They look forward to the good news of Tianwen-1’s arrival on Mars. At that time, this group of people on Earth will also usher in the most exciting and difficult "Mars breakthrough moment."
Whether the mystery of Mars can be unveiled by a Chinese probe, we will wait and see.
China Youth Daily · China Youth Daily reporter Qiu Chenhui Source: China Youth Daily